Electric motor load indicator



y 1952 R. R. PROCTOR ETAL 2,605,304

ELECTRIC MOTOR LOAD INDICATOR Filed Oct. 18, 1947 f? i 15 ID: [a /16:25lc) 2s 2 24 Q 50 I 20 29 H4 P- 4 INVENTORS. RONALD l2.- PROCTOR BYLYNN E. ELLISON Arron/v5 Y Patented July 29, 1952 Ronald R. Proctor,Evanston, and Lynn E. Ellison, Crystal Lake, 111., assignors to The PureOil Company Chicago, 111., a. corporation of Ohio Application October18, 1947, Serial No. 780,648, 7 (Cl. 171-95) K 3 Claims.

This invention relates to an apparatus and method forobtaininginformation on the operating conditions of power consumingmachinery and for aiding in the control and regulation thereof. It hasparticular application in situations which involve analyzingthe'operation of machine tools.

In machining operations, whichusually require use of cutting fluids, aproblem which is universally encountered is that of detecting toolfailure in time to save thetool and avoid substantial faulty cutting ofthe work piece. That is to say, normally a tool can begin to fail, andsuch failure can progress to a fairly acute stage, before it willmanifest itself by an observable depreciation in the quality of thesurface of the work piece. Whether it be failure of the tool or of thecutting fluid used which causes the difficulty, it is highly desirablein any operation to detect incipient failure of either the tool or thecutting fluid, thereby to give the operator time to take correctivesteps.

' The problem, though it has specific application in machiningoperations, also has general application in that it involves detectionof the departure from steady state operation at as early a stage aspossible to permit an operator to take corrective steps. In thetestingof anytool; such as a drill, milling machine, lathe, or anyfofthat type of cutting instrumentoperating at constant feed and speed,failure of the tool or cutting fluid would be reflected by a change fromsteady state operation, such as an increase in the power demand. Where aroutine visual observation of the work is resorted to, detection of thefailure willoften be too late to permit saving of the work or the tool.I

Accordingly, it is a fundamental object of this invention to provide anapparatus and a, method by which an incipient departure from "steadystate conditions ,in power consumption can be detected conveniently. J-

It is a second object of the invention to provide an apparatus forindicating early failure of tools in cutting operations. I

It is another object of theinvention toqprovvide an apparatus and -amethod for testing cutting fluids; c

Other objects and advantages of the invention will in part be obviousand in part appear consuming system from steady state conditions, whichapparatus h'asthe features of construction,

combination of elements and arrangement of parts hereinafter describedin greater detailand which method involves the several stepsandrelationship of the steps to each other for detecting the saiddeparture. I

More specifically, the invention comprisesfan electrical apparatusinvolving a balanced circuit by which a variation in'the consumption ofpower ond side of said balanced circuit, whereby a differential signaldeveloped between the two sides as a result of a condition of unbalancewill give an indication of the magnitude and direction of the. departurefrom' steady state-Scondition.

' The scope of the invention and the construction of the apparatus willbe more clearly understood by reference .to the detailed descriptionbelow and the accompanying drawing in which:

Figure 1 is a schematic diagram of an electric circuit showing anoperative arrangement of elements to accomplish the measurementdescribed.

In the figure, It represents a power supply, shown to be a three-phasealternatingcurre'nt supply, broughtby means of conduits l I to-a loadindicated generally as a machine 12. In one'leg of the power supply,there is placed a resistor 13, preferably having a low resistance ontheiorder of one ohm or a fraction thereof for large'motors and one ohmor more for smally;mo tors. Across the resistor 13, there is connectedthe primary coil Mp of transformer lsi-whichqhas-its secondary coil Mssupplying voltage to onehalf of the-balanced detecting-circuit.Connection is made from coil His byiway of line l5 to plate 16a of tubel6. Return from the cathode I is made by way of resistor ll connected inseries with resistor [8, which returns to the other side of coil I 63.[Filtering condenser?! 9 is "connected between the end of coil 14s andthecathode of the tube l5; similarly,filtering condenser 29 is connectedbetween the end of coil His and a point between the two resistorsll andl8 '3 The second half, or standard portion of the circuit physically ismade substantially" identical with the portion described, but issu'pplie ith 1 an adjustable reference voltage which is 'le'pt constantat any predetermined setting. Referring to the diagram, a standardalternating current voltage is supplied by lines 2! to the primary 22 ofan adjustable-output auto-transformer. A portion of this voltage istapped oif to feed primary coil 23p of transformer 23, thereby applyinga steady voltage to secondary 23s. It .will be .:observed that one .endof secondary flsisconnected'by way "of line 2-4 to :the plate 25a oftube 25. Return from the cathode 250 is made by way of resistors 26 and27 to the other side of coil 23s. Filteringcondenser 2.8 is connectedbetween the end of coil 23s and'the cathode 25c; and in similar:fashion, .filtering' condenser 29 is connected lbetween .the-sendzof icoil 23s and a point between the tWd-resistors 26 and 21. a V I Thetubes l6 and 25 can be any ordinary rec't'itying tubes, and, as a matterof convenience, a double rectifier having both tubes in the same'ienvelope is useful.

:Connected betweenthe junction points of the two ;pairs-of iresistors41, 1%, "and 26, 21, there is :galvanometertll. Thiscanbe a smallmicroammeter, preferably a zero center --reading type in order :thatdeflections in either direction can be rdete'cte'd.

:Acrossthemeter ,orgalvanometer 30, there is :connected a selecting l orcalibrating circuit for setting the range or sensitivity of the 'meter,awhichqconsists of switch :3 I having a plurality --of rpositions :32:33 5M, :and 3 5 forshunting resistors aof'idifieren't values zaroundmeter 30. :It will :be ebserved thatiby inserting various resistors "inthe line :andTby maintaining one 'of themza :vari- .rablefithesensitivity ;of the meter'can 'be adjusted to 32; variety ;'of .levels.:Switch 131, which ."is a odouhle :pole tmulti-position switch, controlsthe flow :of current :to ftransformer122 .and the"filarmentspfcthe'tubes :ltB rand 25 through .its isecon'd -hali:36zbywaysof'line 31-?and connectionstaii.

Theideviceshould be 'i'built'with the "two:halves of the circuitsubstantially identical electrically, so that the zapparatus 62117138'zbroughtto 5a sstable -balanceito :correspond to steadyrstateiconditions.

'mhisi'mvnlveszmaking resistors I1 and 26, and I58 19.11512?!:closelymatched. .It :haszbeen found that walues offabout15000ohms. aresuitableiwhen used with cal-11726 irectifierltube and a?30-'0-i30microampere 'galvanom'eter.

il'he operation -"of the 'device is apparent from -"the. generaldescription of the .circuit, but it should: be noted-that mo'st'success'fuloperation is .iattainediwhen the value-'of sens'ing resistor13 is .setisoithat the voltage "developed across it under -:ricn'mal:operating conditions is "equal to the 'proper prima'ry voltage"for-application to the primary coil 11p :of the liigh ratio step-up''transf'ormer M. r

To consider the operation of the device in-"deitaiL let it be assumedthat power supply is t' furnisliin'g three-phase alternating current toa ":machine 12 which isalathe cutting-a metal work spiecwwhile :using a:given cutting fluid. When thess'urfacerspeed of the :work in themachine is ukept eat a 'constant'ivalue, it will be understood thatrthe'loadzon tthetool will be constant and, consequently, the.loaddemandedfrom thepower supply -will :be :constant. A deviation :fromthe E'steady stateloadwhichrcausesthe :driving motor of .the machine todraw more current indicates iailure -.of the tool, or *a :change in"some :factor eflecting-the cutting operation.

1 As'soon'as the load demanded from the power supply deviates slightlyfrom that required -for steady state operation, the voltage acrosssensing resistor I3 will change, the changed voltage will be applied tocoil 14p and produce a corresponding magnified change in coil I ls oftransformer I4. This magnified voltage is applied to the plate 16a ofrectifier tube I6 and current conducted from the cathode throughresistors I! and I8 :ba'ck' to the'other side or the coil. At the sametime, a reference voltage is'applied through coil 23s to the plate 25aof tube 25 and current returned by way of resistors 26 and 21 to theother sideof-thesaidcoil. The magnitude of the voltage applied to coil23p is set so that the voltage ;drop:across.resistorsi26 and 21 will bethe same as thewoltage drop across resistors l1 and Hi When steady stateconditions prevail. It will be jnotedlthatifthe .voltage drop acrossresistors I1 and 26 is the same, no current Will flow through meter :30and no indication will be obtained therefrom. However, when a deviationfrom 'steadyastate operation occurs and a change in demand on the p'owersupply .l il results, exchange in the current flowing through resistorsH *and 18' willbe reflected by achange .in'voltageacross them, thus*unbalancing the circuit and producinga corresponding'indication ofthemeter 30.

As noted in the description of the meter, adjustment of "the sensitivityof its circuit by the insertion :of a high shunting resistance bymeansof switch 3l 'will make :itpossible to detect very slight deviations inthe ;;p0Wer supply demanded 'by'the machine. I

Itshould also :be noted that the single-phase power source whichsuppliesheater voltage to tubes "t6 and T25 :and transformer .22 through switch36 can be tapped ofi the three-phase. leads I I with .the result that:any 'variation 'of' voltage 'due to supply fluctuations -wi1l a'ctonboth halves .of :the bridge equally so that no indication-will'beapparent on the'meterfiil. Hence, the instrument responds only toload changes.

In the testing of cutting .fluids with the apparatus described, it hasbeen found that the device "will reliably detect failures :in the toolwhich are invisible to the naked eye and require microscopic examinationof -the tool and the work piece to'be located. 'Thus,.it will be'seenthat when .it is desiredto:measurelthe conditions underwhich "acuttingiiuid can "be expected to ffunction .properly,ithe detection ofincipient Ifail- .ureiofthettool serves as a valuable'indicationpi theseverity "of conditions towhich'lthe 'flui'dcan be subjected. 'Inthis'fashion, various cutting fluid compositions' were tested andresults found reproducible to a degree of precision unattainable by anyother means. Conversely, using the same cutting fluid, the performanceof various types of tools 'difiering'in material and in shape can bedetermined, as well as the life expectancy of various tools in cuttingvarious types of material. Y

Thegeneral applicability of the apparatus to the control of alternatingcurrent installations which normally operate understeady stateconditions should be apparent for any change in the loadbn a systemwhich causes a deviation can be readily detected. For example, thedevice can be .used on pumps to detect packing failure ior cloggedlines, and in conveyor systems "to guard against overloading. Thus,although only one specific embodiment :of the apparatus Thas beendescribed in detail, :since changes in .the embodiment can bemade'without departing'from thescope :of theinventiongitris intendedtthatfall matter included in the description or shown in the drawingshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A test apparatus comprising in combination, a power supply to a powerdriven cutting tool undergoing test, detecting means connected to saidpower supply including a resistor, a coil across said resistor to formthe primary of a first transformer, a secondary coil coupled with saidprimary, a rectifier and a first pair of fixed resistors in series insaid secondary coil circuit, a second rectifier and a second pair offixed resistors matching said first pair, a coil across said secondrectifier and said second pair of resistors forming the secondary of asecond transformer, and a primary coil to supply a fixed voltage to saidsecond transformer, and an indicator brid ing said resistors to detectand show the direction and magnitude of any unbalance in the system.

2. Apparatus in accordance with claim 1 in which the indicator isconnected across the resistors at substantially their midpoints.

3. A test apparatus for determining small changes in power undersubstantially constant voltage conditions comprising in combination, apower supply to an electrically powered machine, detecting meansconnected to said power supply including a resistor, a coil across saidresistor to form the primary of a first transformer, a secondary coilinductively coupled with said primary, a rectifier and aresistance-capacitance filter net-work in series therewith, a secondrectifier and a second resistance-capacitance filter net-work in seriestherewith, a secondary coil supplying said second rectifier and aprimary coil to supply a fixed voltage to said second secondary coil andan indicator bridging said resistancecapacitance net-works at their midpoints to detect and show the direction and magnitude of any unbalancein the system.

RONALD R. PROCTOR. LYNN E. ELLISON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

